An important consideration in designing internal combustion engines is minimizing emissions of hydrocarbons expelled from the engines. Even small advances in decreasing the amount of hydrocarbon emissions per vehicle is significant when multiplied by thousands or millions of vehicles.
One source of hydrocarbon emissions is unburned fuel which is exhausted from combustion chambers. A small portion of the fuel located in a combustion chamber may be disposed in crevices in fluid communication with the combustion chamber. These crevices are formed between components defining the combustion chamber such as engine blocks, pistons, seals, cylinder heads and spark plugs. The hard-to-reach fuel located in these crevices may escape a flame front created by introducing a spark into a fuel filled combustion chamber. The unburned fuel may then escape into the atmosphere from the combustion chamber during an exhaust stroke of the engine.
As an example, a spiral-shaped crevice is formed in the gap between the external threads of a spark plug and the receiving internal threads cut into a cylinder head. The present invention is intended to eliminate this crevice.